Alpha amylases are available from many microorganisms living in diverse environments Bacterial sources include Bacillus subtilis, Bacillus licheniformis, and Bacillus stearothermophilus. It should be noted that although each of these sources can yield a thermostable amylase, the enzymes differ substantially in characteristics such as molecular weight, pH optimum, temperature optimum, and calcium ion affinity. In other words, the enzymes from these sources are conveniently grouped together because they hydrolyze starch into malto-dextrins.
U.S. Pat. No. 4,284,722 to Masaki Tamuri, Mitsuo Kanno, and Yoshiko Ishii describes a particular heat and acid-stable amylase made by a Bacillus stearothermophilus organism. The enzyme is characterized as having a pH optimum of about 4 to 6, a temperature optimum of about 65.degree. to 85.degree. C., and a molecular weight of about 90,000.
The Bacillus organism of Tamuri et al. is deposited in the American Type Culture Collection (ATCC) as Bacillus stearothermophilus strains Nos. 31,195-31,199. Other alpha amylases from Bacillus stearothermophilus are reported by Ogasahara et al., J. Biochem, (1970), 67, pp. 65, 77, 83 and Manning et al., J. Biol Chem, (1961) 236, pp. 2952, 2958, 2962.